This application claims the priority of Japanese Patent Application No. HEI 09-173081 filed Jun. 13, 1997, which is incorporated herein by reference.
This invention relates to an additive to a fluidized catalytic cracking catalyst for heavy oil.
A variety of methods are known for obtaining light oil by cracking heavy oil, such as fluidized catalytic cracking (FCC). A great deal of research has been conducted to achieve high yields of the desirable light oil products. It is known to add and mix a catalyst, which acts to promote cracking of heavy components in heavy oil, with a cracking catalyst to improve the yield of light oil.
As such additive catalysts, those composed of alumina, clay and silica have been known to date. However, these additive catalysts are typically accompanied by a problems, such as the cracking of heavy oil not being promoted or the formation of undesirable amounts of coke.
An object of the present invention is to provide an additive catalyst for the cracking of heavy oil, which has relatively high cracking activity for heavy components in the heavy oil with reduced coke deposition.
With a view to attaining the above-described object, the present inventors have proceeded with extensive research, leading to the completion of the present invention.
In accordance with the present invention, there is thus provided an additive catalyst for the catalytic cracking of heavy oil, characterized in that the additive catalyst comprises a large pore zeolite, a mixed metal oxide, clay and a metal oxide, and the total acidity of a portion of said catalyst, said portion being composed of said catalyst components other than said zeolite, is from 0.02 to 0.08 mmol/g.
Specific examples of the mixed metal oxides employed as a catalyst additive component in the present invention can include silica-alumina and silica-zirconia as preferred examples and also silica-containing mixed metal oxides, such as silica-magnesia, silica- titania and silica-boria. In the case of silica-alumina, it is preferred to use one having a silica content in a range of from about 5 to 30 wt. %, preferably from about 10 to 20 wt. %. A silica content higher than this range results in a catalyst having relatively poor hydrothermal stability, while a silica content lower than the above range leads to a catalyst having relatively low cracking activity for heavy components. Silica-aluminas suitable for use in the present invention have, as expressed in terms of physical properties in their calcined form, a specific surface area ranging from about 250 to 450 m2/g, preferably from about 300 to 400 m2/g, a pore volume from about 0.5 to 1.5 cc/g, preferably from about 0.7 to 1.2 cc/g. It is also preferred to use a silica-alumina having a structure wherein silica is bonded in the form of a layer on a surface of alumina as a core. In the case of silica-zirconia, it is preferred to use one having a silica content in a range of from 5 to 30 wt. %, preferably from 10 to 20 wt. %. A silica content higher than this range results in a catalyst equipped with poorer hydrothermal stability, while a silica content lower than the above range leads to a catalyst having lower cracking activity for heavy components. Silica-zirconias suitable for use in the present invention have, as expressed in terms of physical properties in its calcined form, a specific surface area ranging from about 100 to 400 m2/g, preferably from about 120 to 350 m2/g, a pore volume from about 0.1 to 1.0 cc/g, preferably from about 0.2 to 0.8 cc/g. As silicazirconia, it is also preferred to use one having a structure wherein silica is bonded in the form of a layer on a surface of zirconia as a core. Illustrative of the mixed metal oxide are alumina-magnesia, alumina-calcia and alumina-boria in addition to the above described silica-containing mixed metal oxides. In the case of alumina-boria, the content of alumina may be from about 5 to 95 wt. %, preferably from about 10 to 90 wt. %. It is preferred to use one having a structure wherein boria is bonded in the form of a layer on a surface of alumina as a core.
The mixed metal oxides employed in the present invention generally have a specific surface area from about 250 to 450 m2/g, with 300 to 400 m2/g being preferred, and an overall pore volume of from about 0.5 to 1.5 cc/g, with 0.7 to 1.2 cc/g being preferred. One having relatively large pores in a large proportion in its pore volume distribution is preferred. In the present invention, the pore volume A of pores having diameters from 60 to 200 xc3x85 may account for at least 65%, preferably about 75 to 85% of the overall pore volume T, and the pore volume B of pores having diameters of from 100 to 200 A may preferably account for at least 30% of the overall pore volume T. The ratio B/A of the pore volume B to the pore volume A may preferably be at least 0.4, notably 0.45 or greater.
In the mixed metal oxide employed in the present invention, its pore characteristics such as specific surface area and pore volume can be controlled according to conditions for the production of the mixed metal oxide.
The catalyst according to the present invention can be obtained by conventional methods. For example, the catalyst can be obtained by evenly mixing the zeolite, the mixed metal oxide, the metal oxide, and the clay in an aqueous medium and then spray drying the resultant slurry.
Usable examples of the zeolite can include a variety of conventionally known crystalline silicates, for example, crystalline aluminosilicate and aluminometallosilicates containing a metal in their skeleton structures (e.g., crystalline aluminogallosilicate and the like). Particularly preferred are synthetic Y-type zeolite ultrastable Y-type zeolite, ZSM-5 and xcex2-mordenite, all of which are common in crystalline structure with faujasite. It is also preferable to use one containing hydrogen and/or a rare earth metal as cations.
Illustrative of the metal oxide can be silica, alumina, magnesia, zirconia, and titania. Of these, use of silica is preferred.
Examples of the clay can include kaolin, bentonite and kibushi clay. Of these, use of kaolin is preferred. In general, one containing as a primary component one or more of clay minerals such as kaolinite, dickite, nacrite, halloysite and hydrated halloysite is used.
In the catalyst of the present invention, the content of the zeolite can be generally from about 1 to 40 wt. %, preferably from about 10 to 30 wt. %; the content of the mixed metal oxide can be generally from about 5 to 80 wt. %, preferably from about 10 to 60 wt. %; the content of the metal oxide can be generally from about 10 to 40 wt. %, preferably from about 15 to 35 wt. %; and the content of the clay can be generally from about 10 to 80 wt. %, preferably from about 20 to 70 wt. %.
In the portion (i.e., matrix portion) of the catalyst according to the present invention, said portion being composed of said catalyst components other than said zeolite, that is, in the portion composed of a mixture of the mixed metal oxide the metal oxide and the clay, the specific surface area can be from about 35 to 65 m2/g, preferably from about 40 to 60 m2/g, and the overall pore volume can be from about 0.14 to 0.45 ml/g preferably from about 0.20 to 0.40 ml/g. Further, its pore distribution may preferably be biased toward relatively large pores. The pore volume A of pores having diameters of from about 60 to 200 xc3x85 may account for at least 45%, preferably 50% or more of the overall pore volume T, and the pore volume B of pores having diameters of from about 100 to 200 A may account for at least 20%, preferably 25% or more of the overall pore volume T. The ratio B/A of the pore volume B to the pore volume A may be at least 0.4, preferably 0.5 or greater.
The pore characteristics of the portion of the catalyst according to the present invention, said portion being formed of the components other than the zeolite, can be controlled by the kind and content of the mixed metal oxide and can also be controlled by the mixing proportions of the mixed metal oxide, the metal oxide and the clay, production conditions for the catalyst, and the like.
In the catalyst according to the present invention, the total acidity of the portion composed of the catalyst components other than the zeolite is specified to range from about 0.02 to 0.08 mmol/g, with 0.025 to 0.07 mmol/g being preferred. This makes it possible to suppress the deposition of coke and also to obtain middle distillate at a high yield in catalytic cracking of heavy oil. This total acidity can be easily controlled by adjusting the kind, composition and/or the like of the matrix portion formed of the mixed metal oxide, the metal oxide and the clay as the catalyst components other than the zeolite.
For the preferred production of the catalyst of this invention, a gel of the zeolite, the clay and the mixed metaloxide is added to a sol solution of the metal oxide such as a silica sol solution, and the resulting mixture is uniformly stirred to prepare a dispersion. In this case, the average particle of the zeolite can be from 0.1 to 1 xcexcm; the average particle size of the clay can be from about 0.5 to 5 xcexcm, with 2 to 3 xcexcm being preferred; and the average particle size of the mixed metal oxide can be from about 0.5 to 10 xcexcm, with 3 to 7 xcexcm being preferred. Further, the total solid concentration of the dispersion can be from about 10 to 50 wt. %. with 20 to 30 wt. % being preferred.
The dispersion prepared as described above is next spray dried. Its drying temperature is from about 180 to 300xc2x0 C., preferably from about 200 to 270xc2x0 C. By this spray drying, the catalyst of the present invention is obtained in the form of a powder. The average particle size of this powder ranges from about 50 to 80 xcexcm, with 55 to 70 xcexcm being preferred. The dry product obtained as described above can be used after heating it to about 300 to 700xc2x0 C., preferably about 400 to 600xc2x0 C. as needed. Moreover, this powdery catalyst can be formed, if needed, by extrusion or the like into a formed product of a granular, spherical, cylindrical, rod-like or similar shape.
The catalyst according to the present invention can be used by dispersing it in the form of fine powder in heavy oil. As an alternative, it can be employed by mixing the same in a conventionally-known cracking catalyst for heavy oil. Preferably, the catalyst of the present invention can be used by mixing it in the form of powder in an FCC catalyst. An FCC catalyst is composed of a porous inorganic oxide and zeolite. Usable examples of the porous inorganic oxide can include silica-alumina, silica- zirconia, and silica magnesia. The catalyst according to the present invention can preferably be applied to FCC catalysts, especially, those composed of zeolite, silica, alumina and kaolin. The content of the catalyst of this invention in each FCC catalyst may range from 2 to 30 parts by weight, preferably form 4 to 20 parts by weight per 100 parts by weight of the FCC catalyst.
When catalytically cracking heavy oil by using such an FCC catalyst, the reaction temperature may range from 470 to 550xc2x0 C., preferably from 480 to 520xc2x0 C. The catalyst/oil ratio can be from 3 to 6 wt/wt, preferably from 4 to 5 wt/wt.
Usable examples of the heavy oil can include various feed oils as well as their atmospheric distillation residues and vacuum distillation residues. In addition, solvent-deasphalted oil, solvent-deasphalted asphalt, shale oil, tar sand oil, liquefied coal oil and the like can also be used. It is also possible to use those available by blending vacuum gas oil (boiling point range: 343 to 600xc2x0 C.) in the above-described heavy oils.
As the total acidity of the portion (matrix portion) of the catalyst components other than the zeolite is limited to the specific range, the catalyst according to the present invention has excellent cracking activity for heavy oil. By conducting a catalytic cracking reaction of heavy oil with the catalyst of this invention added therein, naphtha and middle distillate can be obtained in high yields. Moreover, the deposition of coke can be significantly reduced in the catalytic cracking of heavy oil, thereby achieving prolongation in the service life of a cracking catalyst.